A drug delivery device which includes a first housing part, a second housing part, a button, a drug expelling mechanism, a graduated plate, a circuit board and a pressing rod. The button is connected to the first housing part. The drug expelling mechanism is disposed inside the second housing part, and includes a dose setting member which is rotatable and configured to set a drug dose to be expelled. The graduated plate is disposed inside the first housing part and connected to the button, and includes a first conductive element and a plurality of second conductive element disposed on a surface thereof. The plurality of second conductive elements are arranged in interval and the first conductive element is electrically connected to the plurality of second conductive elements. The circuit board is disposed inside the first housing part and connected to the dose setting member. The pressing rod is inserted through the graduated plate, and includes an end connected to the button and the other end movable on an axial direction to trigger the actuating switch.
